Contact device



Aug. 7, 1956 J. J. A. ROBILLARD 2,758,263

CONTACT DEVICE Filed Oct. 5, 1952 INVE/W'OR Em Jams flea/1.1.5 Roe/u 3RD United States Patent CONTACT DEVICE 'Jean Jules AchilleRobillard,Hagersten,Sweden, assignor to Telefonaktiebolaget I. M Ericsson, F'Stockholm, Sweden, a corporation-of Sweden Application October 3, 1952, Serial Nb. 313,025 Claims priority, application Sweden January 8, 1952 12 Claims. .(Cl. 31.7-235) The present invention relates to contact devices of the 'kind used toproduce such point contacts as are required for transistors and crystal contact rectifiers.

In transistors as hitherto known, electrodes consisting of fine pointed wires .are'used to obtain the closely spaced contact points with small area on agermanium crystal, which are required for the desired function. These transistors with point electrodes have however many disadvantages, such as:

1. Lack of function-stability owing to the mechanical instability .of the point electrodes, .the position and .contact pressure of which may vary due to for example shocks, vibrations and thermionic expansion. There is further the risk of oxidation of the crystal and the point electrodes.

'2. Strong noise, partlydepending on 'the imperfect contact :between the points and 'the crystal.

3. The current supply through the extremely fine point electrodes is limited.

4. Difiicult production, since the 'mounting of the electrodes must be eifectedwith the greatestprecision under a microscope and with the help of accurate adjusting means, so called micromanipulators. In spite of this, 'it 'is not possible to be sure to succeed every time, since all the points of the surface of the crystal are not suitable for transistoreffect and -it -is very cumbersome to locate the suitable points. A very small movement made 'by an electrode is sufficient to change the qualities of the transistor or even to make it useless. These circumstances make it very diflicult -to produce on a large scale.

5. Lack of homogeneity. For the same reasons as disclosed above in point4 it is 'diflicult to obtain transistors with approximately equal characteristics. 9

The preceding is also true to a certain degree with regard to crystal contact rectifier-s, which are also provided with point electrodes.

The present invention relates to a contact device to be substituted for point electrodes on the crystal surface and wholly or partly eliminating the above mentioned disadvantages. According to a now preferred embodiment of the invention, this is achieved by the contact device forming a great number of contact points and being characterized by a close-meshed grid placed on the surface and by a conducting layer applied by thermionic evaporation on the grid and the parts of the surface exposed through the meshes of the grid, said layer being insulated from the grid.

The invention will be described more indetail in connection with the accompanying drawing, in which Fig. 1 shows a plan view of a grid,

Fig. 1a shows a section of the grid,

Fig. 2 shows a section of a contact device for a transistor,

Fig. 3 shows a contact device for a contact rectifier, and

Fig. 4 shows a perspective drawing of a transistor according to the invention.

As grid which is shown in Fig. 1, a very fine screen 2,758,263 Patented 1 7, 11 956 of metal, suitably copper, and of the same kind :as is used for production of electrotypes for-typographical purposes, mayadvantageonsly be used. .Such screens are produced by electrolytic precipitation and may suitably havean average thickness of 40, andcomprise about 20 meshes per mm each mesh having a diameter 'of ca. a. Such screens are produced on a large scale and .are commerciallly available.

.In the contact device shown in Fig. .2, 1 designates a germanium crystal, 2. a grid according to .Fig. 1 3 .an insulating layer, 4 a layer of contact metal and 5 a base electrode soldered to the germanium crystal.

The insulating layer 3 on .the ,grid2 consists -.of a thin layer of silicon dioxide produced by vacuum evaporation tOf silicon dioxide powder :in the following manner: The screens are well cleaned by washing and electrolytic polishing at low current density, and fastened on a glass plate placed -in a vacuum vesselabout 20 cm. .abovecrucibles containing silicon dioxide powder. Silicon dioxide .evaporatesat about 2300" C. and apressure of :10" mm. :Hginsuoh quantity, that an insulating :layer is formed hav- .ing a thickness vsui'licient to resist voltages to which the device is exposed in operation. The side facing the glass plate .is not covered with insulating coating. The glass plate itself is prepared so that no silicon dioxide layer is formed .on it.

The grid is placed with the uncoated surface against the germanium crystal 1, :whereaifter-a contact rmetal, suitably tungsten, is evaporated over the grid :and the .parts of the germanium crystal exposed through the meshes of the grid. The evaporation :is effected by means :of :a numfiber of tungsten wires heated electrically close :to the grid. The evaporated layer 4 is .made 1 to 2 thick. The -tongue 2a of the :grid according :to Fig. 1 is .protected against evaporation of both silicon dioxide and tungsten .and :is used .as :supply electrode for the contact points formed by the parts of the grid lying against the surface of the germanium crystal. Each one of the meshes of the grid forms together with a vacuum 'evaporated contact point a contact pair, with' which the tranfSlStOItDlTeCt can be obtained. The different contact pairs :are connected in parallel .to each other and thus function .mostly independent of .each other. The distance between the contact points and .the respective meshes, which .is importantfor the function of the transistor, determined by the thickness of the insulating layer, which can easily be varied by evaporating different quantities of silicon dioxide.

Owing to the great number of contact points a more uniform product is obtained, the distribution of good and bad contact points being such, that the average value is fairly constant for the whole transistor, and furthermore, the load capacity of the transistor is greater. The vacuum evaporated contact points are very stable and are not sensitive to shocks, vibrations and moderate changes of temperature. The contact between the germanium body and the vacuum evaporated contact points is further very intimate, which results in a reduction of noise.

The contact device according to Fig. 3, which is intended for rectifiers, differs from that shown in Fig. 2 only by the grid being completely insulated, so that only the vacuum evaporated contact points make contact with the germanium.

Fig. 4 shows a perspective View of a section of a transistor manufactured according to the invention. The germanium crystal 1, soldered to the base plate 5, is inserted under pressure in a plastic envelope 6, in the bottom of which there is a contact 9 for the base plate. The grid 2, insulated as described in connection with Fig. 2, is placed on the upper surface of the crystal 1, activated in a known manner, and pressed against said surface by means of a plastic ring 7, so as to be in close contact with the surface. Over the parts of the grid exposed through apertures 11 and 12 and a contact 8, there is disposed a tungsten layer evaporated in the same manner as described above. The contact 8 is the outer connection to the vacuum evaporated contact points, whereas the contact to the grid is obtained by the tongue of the grid projecting through an aperture 10 in the envelope 6. The aperture 12 may be sealed with plastic.

A transistor made according to the example of Fig. 4 had a diameter of 6 mm. and a height of 4 mm.

Transistors and contact rectifiers made according to the invention are very suitable for production on a large scale. The different vacuum evaporating processes may be effected for a great number of elements simultaneously and the mounting is considerably simpler than for transistors with point electrodes.

I claim: a

l. Contact device useable in crystal contact rectifiers and transistors to obtain a great number of point contacts on a surface, said point contacts being connected in parallel with one another, characterized by a fine-mesh conducting grid placed on the surface of a crystal and by a conducting layer applied by thermionic evaporation on the parts of the surface exposed through the meshes of the grid, said layer forming a number of point contacts with the surface and being insulated from the grid.

2. Contact device according to claim 1 especially for transistors, characterized in that the part'of the grid facing said surface is not insulated and makes contact with the surface.

3. Contact device according to claim 1, characterized by the grid consisting of a screen of the kind used to produce electrotypes for typographical purposes.

4. Contact device according to claim 3, characterized by the screen having at least 20 meshes per rmnf said meshes having a size of 75 1..

5. Contact device according to claim 1, characterized by the grid being insulated from the conducting surface by means of a layer of vacuum evaporated silicon dioxide.

6. A contact device usable in crystal contact rectifiers and transistors, comprising a crystal having a plane surface, a layer having a multiple of perforations supported by said plane surface and a conductive second layer on said first layer, said second layer being insulated from the first layer and filling said perforations to form an-intimate contact with the areas of the crystal surface exposed =by said perforations in the first layer thereby forming a multitude of contact points between the second layer and the crystal surface, all connected in parallel.

7. A contact device according to claim 6 in which said perforated layer comprises a skeleton of conductive material and an insulating coating surrounding said skeleton at least on its surfaces in contact with said second layer.

8. A' contact device according to claim 6 for use in crystal contact rectifiers, in which said perforated layer comprises a skeleton of conductive material and an insulating coating surrounding the skeleton on its surfaces in contact with said second layer and its surfaces in intimate contact with said crystal surface;

9. A contact device according to claim 6, characterized by said perforated layer being insulated from the crystal surface and the conducting surface by a layer of a vacuum evaporated silicon dioxide.

10. A contact device usable for example in crystal contact rectifiers and transistors comprising a crystal having a plane surface, an electrically conductive layer having a multitude of perforations disposed on said plane surface in intimate contact therewith, and a second jconductive layer on said first layer, said second layer being insulated from the first layer and in intimate contact with the areas of the crystal surface exposed by the perforations in said first layer thereby forming a multiude of contact points between the second layer and the crystal surface, all connected in parallel.

11. A contact device according to claim 10, wherein the said first conductive layer is in direct contact with the crystal surface. v

12. A contact device according to claim 6, wherein the said perforated layer is insulated from the crystal surface in addition to being insulated from the second conductive layer.

References Cited in the file of this patent UNITED STATES PATENTS 2,046,686 Kannen'berg July 7, 1936 2,345,122 Herr-mann i Mar. 28, 1944 2,386,218 Kotterman Oct. 9, 1945 2,444,385 Thompson June 29, 1948 2,595,052 Casellini Apr. 29, 1952 FOREIGN PATENTS 500,180 Great Britain Feb. 3, 1939 500,342 Great Britain Feb. 7, 1939 500,344 Great Britain Feb. 7, 1939 529,754 Great Britain. Nov. 27, 1940 

